Add API for VF Management port in OVN-K

Issue and Design: https://github.com/ovn-org/ovn-kubernetes/blob/master/docs/design/shared_gw_dgp.md 

Upstream PR: https://github.com/ovn-org/ovn-kubernetes/pull/3160 

Document that describes how to use the mgmt port VF rep for hardware offloading: https://docs.google.com/document/d/1yR4lphjPKd6qZ9sGzZITl0wH1r4ykfMKPjUnlzvWji4/edit# 

==========================================================================

After the upstream PR has been merged. We need to find a way to make the user experience configuring the mgmt port VF rep as streamlined as possible. Basic Streaming that we have committed to is improving the config map to only require the DP resource name with the MGMT VF in the pool. Also OVN-K will need to make use of DP resources.